Lets just say Jinbe joins as nakama and Weak-hoshi did not tag along. What we have is a formidable opponent in the waters for those who would dare to challenge the SHP to battle in the middle of the sea.
I mean what Jinbe can do is to take a dive, move to the underneath of the foe's ship, pulls a Fishman Karate move which punctures the hull through and through, comes back up onto Sunny-go and the crew can continue to journey into New World without breaking a single sweat.
Yup, am aware that such a victory is lame (with a capital L,A,M and E) but this is possible unless the foe has an ace up in their sleeves to deal with underwater opponents / attacks. Surely the monster trio will be bored, REAL bored... and will start to question their decision in taking Jinbe in the first place (fufufu... just kidding!).
Many are predicting and looking forward to the fight with Smoker-san when Sunny-go surface for the first time in the New World. As that coming into reality, Smoker-san and Tashigi gets pumped up to face off against Luffy and Zoro respectively. Then as their ships come face-to-face (or rather bow-to-bow), Jinbe did the above moves and pull an easy victory over Smoker-san, with the man staring at the Sunny and go "MUGIWARA! Omae!!!@£$&%£" Fufufu...
Lastly, a toast to my first blog, regardless it being successful or otherwise, KANPAI!!